1. Field of the Invention
The present invention relates to a rock blasting method, in which one or more air bladders each having a diameter less than that of a loading hole are embedded in loading holes, so the explosive power of explosive is uniformly distributed over a rock due to an increase in the specific surface area of blasting, thereby reducing blasting vibration and noise, the loading length of explosive is increased by an amount corresponding to the volumes of the air bladders, thereby increasing a projection area toward the free face of the rock, and the amount of explosive consumed is decreased by an amount corresponding to the volumes of the air bladders, thereby conserving explosive.
2. Description of the Prior Art
For conventional rock blasting methods widely used, there are a general rock blasting method in which a rock is blasted with a blasting hole stemmed with a stemming material after the blasting hole is loaded with an explosive, a deck loading type blasting method in which a rock is blasted with explosives and stemming materials alternately arranged in a blasting hole, and a pre-splitting blasting method for smoothing a tangential surface.
Of the conventional rock blasting methods, in the general blasting method, blasting is carried out, with initial explosives 2 and primers 3 and ANFO or bulk explosives 4 being loaded in loading holes 1 and the loading holes 1 being stemmed by stemming materials 5. However, in this conventional rock blasting method, the initial explosives 2 are concentrated in the lower portions of the loading holes 1, so blasting vibration and noise are great, a small rock may fly to the outside, an excessive number of boulders are produced due to the relatively longer length of each stemming material 5 and weak explosive power applied, and the explosives are excessively consumed due to the excessive use of explosives.
In order to solve the problems of the conventional blasting method, a deck loading type blasting method, as depicted in FIG. 1A, was proposed. By the deck loading type blasting method, a rock is blasted with a blasting hole 1 loaded with an initial explosive 2, a primer 3 and an ammonium nitrate fuel oil (xe2x80x9cANFOxe2x80x9d) or bulk explosive 6 and with stemming materials alternately disposed between the explosives 6. In this conventional rock blasting method, blasting is carried out with a plurality of primers 3 loaded in all the loading layers and explosives sequentially detonated so as to break a rock.
The second conventional rock blasting method suffers from the problems that primers are required at a number corresponding to the number of loading layers, thereby increasing a blasting cost, it is difficult to alternately load ANFO or bulk explosives 6 and the stemming materials 7, thereby causing blasting work to be ineffective and uneconomical, and the same amount of explosive is used, thereby hardly reducing blasting vibration.
As shown in FIG. 2, the conventional rock blasting methods are problematic in that the explosion length of blasting is limited to the length of explosive in the loading hole and the length of the stemming material xe2x96xa11 in comparison with the length of the loading hole, so the ANFO or bulk explosive 4 is concentrated in the lower portion of the loading hole and deeply loaded in the loading hole, thereby increasing blasting vibration.
Additionally, a small rock forming portion xe2x80x9cAxe2x80x9d situated under the a fracture boundary line L is broken into small rocks because of strong explosive power applied thereto, while a boulder forming portion xe2x80x9cBxe2x80x9d situated over the fracture boundary line L is relatively large in accordance with the conventional rock blasting method and broken into boulders because of weak explosive power applied thereto. Accordingly, an additional blasting is necessary to blast the boulders, so the implementation of the conventional rock blasting method is inconvenient and requires a high cost.
In order to solve the above problems, the inventor of the present invention filed a rock blasting method using air bladders inserted into a blasting hole so as to form artificial free faces.
This conventional rock blasting method is a technique in which air bladders and explosives are alternately loaded in a loading hole. In the conventional rock blasting method, explosives contained in a container having a predetermined shape are employed, the air bladders each have a diameter equal to or slightly less than that of the loading hole, and the air bladders are inserted into the loading hole while supporting the explosives. Accordingly, this conventional rock blasting method is advantageous in that loading length of explosives is increased, so the amount of explosive consumed is reduced, blasting noise is considerably attenuated and the production of boulders can be prevented.
However, in this conventional rock blasting method, the air bladders each having a diameter equal to or slightly less than that of the loading hole are employed, so it is not easy to insert the air bladders into the loading hole because the air bladders may be ruptured while being inserted into the loading hole.
Additionally, powder-state ANFO explosives or gel-state explosives should be wrapped when the powder-state ANFO explosives or gel-state explosives are loaded in the loading hole, and the air bladders are precisely and tightly inserted into the loading hole, thereby requiring a long period of time for loading explosives and air bladders in the loading hole to carry out blasting.
Additionally, in this conventional rock blasting method, the explosives and the air bladders are vertically separated and a loading layer containing a primer explodes neighboring loading layers by a sympathetic detonation phenomenon. Accordingly, a larger amount of explosive power is concentrated on the wall of the loading hole and a small amount of explosive power is exerted on the boundary between the explosives and the air bladders. Furthermore, the neighboring loading layers are spaced apart from the loading layer containing a primer. As a result, when explosives having a low detonation speed are employed, the detonation effect is not transmitted to the neighboring loading layers, thereby causing the misfiring of explosive.
The present invention provides an improved blasting method that has other advantages as well as the advantages of the conventional rock blasting methods. That is, in the rock blasting method of the present invention, one or more air bladders each having a diameter less than that of a loading hole are embedded in loading holes, so the air bladders can be easily inserted into the loading hole, powder-state ANFO explosive or gel-state bulk explosive can be easily loaded in the loading hole, the explosive continuously and tightly fills the space between the wall of the loading hole and the air bladders to improve a sympathetic detonation function, and the explosive power of explosive is uniformly distributed over the loading hole.
Hereinafter, a xe2x80x9cfree facexe2x80x9d designates the surface of a rock in contact with the external environment, such as air or water, and considerably affects the blasting of the rock. A blasting effect is increased depending on the number of free faces and the relative positions of the explosive and the free face. This is because the free face has no resistance and a larger amount of explosive power is exerted on the free face. A xe2x80x9ctotal pressurexe2x80x9d designates force that unit explosive exerts on a loading hole. A xe2x80x9cspecific surface areaxe2x80x9d designates the area of a rock on which explosive power is directly exerted. A xe2x80x9csympathetic detonationxe2x80x9d designates a phenomenon that different explosives are detonated through a medium, such as air, water or the like, when an explosive is detonated. A xe2x80x9cburdenxe2x80x9d designates a shortest distance between the free face of a rock and the center of an explosive.
Accordingly, the present invention has been made keeping in mind the above problems occurring in the prior art, and an object of the present invention is to provide a rock blasting method using air bladders embedded in loading layers, in which one or more air bladders each having a diameter less than that of a loading hole are embedded in one or more loading layers to form one or more artificial air layers in the loading hole, so the explosion length of blasting is increased and the explosive power of blasting is uniformly distributed over the rock and the loading hole, thereby attenuating blasting vibration and noise.
Another object of the present invention is to provide a rock blasting method, in which one or more air bladders are embedded in explosive layers, so the amount of explosive is reduced by an amount corresponding to the volumes of the air bladders, thereby conserving explosive.
A further object of the present invention is to provide a rock blasting method, in which the explosion length of the explosive is increased due to the air bladders embedded in the explosive, so the total pressure of blasting is increased due to an increase in projection area toward the free face of the rock, thereby easily breaking a rock, and the length of a stemming material is shortened, thereby considerably reducing the amount of produced boulders.
A still further object of the present invention is to provide a rock blasting method, in which the ANFO or gel-state bulk explosive in the form of powder compactly fills the loading hole, so the sympathetic detonation function of the ANFO or gel-state bulk explosive is increased, thereby preventing the misfiring of explosive.
In order to accomplish the above object, the present invention provides a rock blasting method using air bladders embedded in explosives, comprising the steps of: drilling a plurality of loading holes into a rock to predetermined depths in a predetermined arrangement; loading the loading holes with a plurality of initial explosives, a plurality of primers and a plurality of explosives in such a way that one or more air bladders are inserted into each of the loading holes and surrounded by the explosives; stemming the loading holes with stemming materials in the portions of the loading holes situated over the explosives; and detonating the primers so that the initial explosives and explosives are blown up; whereby the loading lengths of the explosives are increased in proportion to the lengths of the air bladders so that a projection area formed on the free face of the rock is increased.